The present invention relates, in general, to a fabric packing, and in particular to a wire cloth packing for a vapor-liquid countercurrent column.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Packed columns are widely used in distillative separation technology, involving a flow of a liquid phase and a vapor phase in opposite directions which are brought into intimate contact to realize a mass transfer between both phases. Mass transfer devices are referred to, e.g., as distillation columns or rectification columns. Mass transfer between liquid and vapor takes place at the interface of both phases. In order to establish and maximize the interface, separating internals are mounted in the distillation columns, like, e.g. mass transfer trays, random packing material, or orderly packings. Orderly packings are hereby understood as geometric arrangements of formed sheet metal layers or fabric layers which are fixedly secured in the mass transfer apparatus. The packings exhibit a large and specific mass transfer surface and a low pressure loss at the same time. The geometry of the packing allows that the specific mass transfer surface and the pressure loss of the packing can be tailored in a desired fashion and suited to the desired separation task.
Fabric packings have been made commercially available by various companies such as Sulzer, Montz or Koch-Glitsch. Fabric packings distributed by the company Sulzer have designations BX or CY and relate to packings made of folded or undulating sheets of fabric layers. Occasionally, additional perforations are punched in the fabric layers. These types of fabric packings have sufficient separation capacity and low specific pressure loss. Fabric packings are predominantly used for separation under a high vacuum and slight liquid load, like e.g. during distillation of volatile oils, fatty acids, or fatty alcohols, because the fabric packings utilize the capillary effect to sufficiently wet the surface with the used materials. Fabric packings are, however, generally unsuitable when great liquid load is involved. As a consequence of the construction of such fabric packings and the involved liquid guidance, the gas load of the packings is limited, and excessive gas load causes flooding of the packing and thus malfunction of the mass transfer apparatus. This is also referred to as capacity of the packing. A measure for the capacity of a packing is the F-factor which is based on gas velocity in the apparatus and the root of the gas density.
Commercially available fabric packings flood in dependence on geometric data and process conditions, like, e.g., pressure in the apparatus, at F-factors of 1.5 to 2.5 Pa0.5.
U.S. Pat. No. 5,607,743, issued Mar. 4, 1997, discloses a metallized three-dimensionally deformed gauze which can be used as packing material for columns, catalysts and catalyst supports. The open meshes of the filigree-type network structure of the electrically conductive gauze are formed from the meshes, extended by deep drawing, of a woven fabric or of a knitted fabric, e.g. of a cross-laid fabric fixed by means of extensible filling threads, of a split-knitted fabric, of a woven fabric or, in particular, of a knitted fabric. The gauze has a base which is provided with a large number of uniformly arranged elevations and depressions in the shape of steps with a round or angular base area. The elevations have a flat plateau at the top and the depressions have a flat bottom to enable a good adhesion between the core material and the applied facings.
European Pat. Appl. No. EP 1 033 168 A1 describes a packing of wire mesh, providing a mass transfer between individual layers of the packing. The layers are interconnected to enable a mass transfer between the layers. This type of fabric packing is relatively complex and complicated to manufacture.
European Pat. Appl. No. EP 0 416 649 A2 describes oriented column packings, using stacked layers, with each layer consisting of vertical walls of yielding, non-metallic, capillary-active material which is reinforced by a braided armoring of rigid material. The walls are shaped as corrugations oriented obliquely to the vertical. This column packing has shortcomings as result of the requirement for providing an additional braided armoring so as to ensure enough stability of the arrangement, because installation of a braided armoring is difficult to implement.
Japanese Publ. No. JP 09 177725 A describes a packing layer having contact plates provided on both sides with projecting parts, with the whole plate having a undulating configuration in both spatial directions. This construction has shortcomings because depending on the wave length the number of wave valleys and wave crests, and the number of projecting parts is fairly high, when a larger fabric packing is involved. Also the number of contact points between two fabric layers becomes very high. In the event, certain applications require a smallest possible mass transfer between fabric layers, the multiplicity of contact points renders this approach unsuitable.
German Offenlegungsschrift DE 32 22 892 A2 discloses a packing for an exchange column, including metal sheets which are disposed in parallel relationship and touch each other in some places and which are provided on at least one side with a plurality of projections and/or indentations. Their height or depth, respectively, is in the order of magnitude of a millimeter and the spacing therebetween is about in the same order of magnitude. These types of sheets have a surface area which is smaller than a tightly meshed fabric so that these packings have oftentimes an inadequate F-factor.
It would therefore be desirable and advantageous to provide an improved packing which obviates prior art shortcomings and which has an increased capacity, without encountering a loss in the separation capacity or increase in pressure loss.